Refrigerant gases containing chlorine, for example difluorodichloromethane (known as "R12"), have been phased out of use in new refrigeration systems for their harmful effects on the environment. Tight regulatory controls have been imposed governing the reuse and reclamation of such refrigerants.
As a result of the new regulatory standards, it has become common to find refrigerant systems that are contaminated by additions of other more readily-available refrigerants. A common "shade-tree" mechanic technique for repairing an automotive refrigeration system is to add R134a or R2 to an R12 system. R134a is now a commonly available non-chlorinated refrigerant, whereas R12 and R22 are not available. Many cars in the southern and western parts of the United States now contain unoriginal mixtures like two-thirds R12 and one-third R22. Similarly, in the past, it was known that an old refrigerator could be "juiced" to make it work a little while longer. The result in either case is an adulterated mixture of refrigerants, which plays havoc with the current requirements for reclaiming and recycling all chlorinated refrigerants. Currently, regulations permit contamination of only 0.5% in reusable, reclaimed refrigerant.
Thus, there presently exists a need for an instrument that HVAC and MVAC technicians can use to analyze refrigerants for identity of refrigerants and their purity.
One prior attempted solution to the problem is disclosed in U.S. Pat. No. 5,498,873. That solution, based on infrared absorption, was incomplete in a number of respects. The technique is similar to Near Infra-red Spectroscopic (NIR) techniques that have been used on contamination detection on critical space hardware. In practice, all species of refrigerant containing a hydrogen, such as the HCFC's, are easily distinguishable. The major difficulty is that if the two refrigerants were different in Cl or F, but contained the same number of H's on each carbon, then the NIR spectra are not easily distinguishable. The refrigerants R20, TCA, and TCE, each containing one or more hydrogens, are easily distinguishable. In contrast, both R113 and R11 contain no hydrogens and show no spectra in the NIR. Further, TCA and R141b, each containing three hydrogens on one carbon, are very nearly indistinguishable in the NIR. Thus there are significant drawbacks in using NIR for identification of a specific refrigerant.
In contrast, it has been found that the indices of refraction of the refrigerants in the liquid state may be readily used to separate out the species by that property. Index of refraction is defined as the angular change in a beam of light passing through the interface of two different substances. The technique of using index of refraction is based on the fact that each refrigerant has a different atomic composition and therefore a different index of refraction. Since the index of refraction is linear with respect to any two components, fairly accurate estimates of two component mixtures can be made.
A difficulty arises, however, in obtaining a reliable measurement of the more volatile refrigerants and comparing that to known values. Good control of temperature and pressure are required. Commercial index of refraction measuring instruments, such as the Abbe refractometer, already exist for liquids; but there are no instruments available which are capable of handling volatile species, such as R12, R22, etc. Hence, an instrument which can be used to perform index of refraction measurements on the volatile refrigerants in standard containers and refrigerating systems is required.
Thus a need presently exists for an instrument which can measure the index of refraction of all the comnmonly-available refrigerants and can be mounted on any standard connection to an AC system or bottle. The instrument must be temperature controlled to establish the index measurement for each specific refrigerant. These temperatures will be established beforehand, making the measurement very straight-forward for the technician making the measurement.
The two refrigerants closest in index of refraction are R12 and R123, which have indices of 1.2870 and 1.2754, respectively. Thus, measuring index of refraction to 4 significant figures will be a necessity.
A refrigerant monitor must be small and rugged enough for a technician to carry the unit to the equipment requiring a sample to be analyzed to determine which refrigerant and to what purity level was currently contained in the equipment.